Running Dukematches in Multiplayer over the net can require port forwarding, especially if you want to host games.
Some routers automatically do this for you (Port Triggering) but most will require some manually configured Port Forwarding.

TIPS:
- If you are running a firewall other than Windows standard, you should turn it off when playing Duke 3D (unless you really know how to configure it to allow it to work).
- If Windows asks when Duke is launching if you want to allow it through the firewall, make sure you select Allow.
- If there are more than one of you at the same home (ie connected to same router) use different ports in Duke Matcher and forward them to your respective PCs IP Addresses in the router (e.g. Player 1 - 23513/8501 and Player 2 - 23514/8502).
- If you are struggling to understand how to do this, come join and try anyway, it may work!